This page describes an older version of the product. The latest stable version is 14.5.

Custom Change

A custom change operation lets the user implement his own change operation in case the built-in operations (increment, add, remove, set, etc.) do not suffice. This is a very powerful capability but it must be used with extreme caution.

Implementing and Using a Custom Change Operation

The implementation should extend the abstract CustomChangeOperation class and implement both the getName and change methods.
See below an example of a change operation which multiplies an integer property value:

With Java 8 lambda syntax the above can be done in a simpler way and without extending the CustomChangeOperation interface:

gigaSpace.change(query, new ChangeSet().custom("multiplyInt", (entry) -> {
//Assume this is an integer property, if this is not true an exception will be thrown
//and the change operation will fail
int oldValue = (Integer)entry.getPathValue("votes");
int newValue = oldValue * 2;
entry.setPathValue("votes", newValue);
return newValue;
}));

The Name of a Custom Change Operation

The custom operation is treated like the built-in change operations (in fact the build in implementations are using the same mechanism), therefore the operation should have a unique name which is used in all the relevant places as described in the Change API Advanced Page, such as configuring which operations are supported by a SpaceSynchronizationEndpoint implementation, using it inside space and replication filters to identify which custom change operation is executed, etc.

Mandatory Implementation Requirements

When implementing a custom change operation, the following guidelines must be followed:

The provided MutableServerEntry is wrapping the actual object which is kept in space, therefore it is crucial to understand when a value is retrieved from the entry
it points to the actual reference in the data structure of the Space. The content of this reference should not be changed as it will directly affect the object in Space and will break data integrity, transaction management and visibility scoping (e.g. transaction abort will not restore the previous value). Changing a value should always be done via the MutableServerEntry.
Moreover, if you want to change a property within that value by invoking a method on that object (e.g. if the value is a list, adding an item to the list), you must first clone the fetched value, and then invoke the method on the cloned copy. Otherwise, you will change the existing data structure in the space without going through the proper data update mechanism and will potentially break data integrity.

Below you can find an example that adds the element 2 into an ArrayList that exists in the entry under a property named “listProperty”. The result sent to client (if requested) is the size of the collection after the change. Note that we clone the ArrayList before modifying it as explained above.

getPathValue, setPathValue operations support nested paths, it will traverse on properties and map keys if the path contains ‘.’ in it (e.g. “myPojo.mapProperty.key”)

When using a replicated topology (e.g. with backup space instances, gateways, mirror) the change operation itself is replicated (and NOT the modified entry). Hence, it is imperative that this method will always cause the exact same affect on the entry (assuming the same entry was provided). For example it should not rely
on variables that may change between executions, such as system time, random, machine name etc.
If the operation is not structured that way, the state can be inconsistent in the different locations after being replicate.

Space Security

Custom change operation lets you run custom code on the space, hence the space security privilege required in order to execute a custom change operation is EXECUTE (the same role which allows executing space tasks).

Custom Operation and Space Integration Points

Using a custom operation with a Replication Filter, Space Filter and Space Synchronization Endpoint is supported
and behaves the same as the built-in operations. You can get a reference to the instance of the CustomChangeOperation by checking its name (or instanceof) and casting to the specific type.